For safe flight it is useful to know the location of the aircraft relative to the airport, both in the air an on the ground. In the air, the relative position of the aircraft relative to airport aids in landing the aircraft. On the ground, knowing the position of the aircraft relative to the airport runways, taxiways, etc., aids in ensuring the aircraft is in the desired position, and to avoid incidences such as runway incursions.
Aviation governing bodies have expended a large amount of resources to develop systems to aid in knowing the location of the aircraft relative to the airport and its runways, especially runway incursions as airports have gotten busier. However, the current systems require complicated radar systems, global positioning systems (GPS), detailed airport databases, and communication methodologies. Many of these systems are dependent on resources external to the aircraft and communication with the aircraft, making them subject to loss of utility if the communication is lost. Further, many of the GPS based systems require expensive receivers installed on the aircraft and the purchase and maintenance of aircraft physical survey databases describing runway position. Further, such systems will not provide any helpful information at an airport unless that airport is in the airport survey database.